The field of the present invention relates to the delivery of energy impulses (and/or fields) to bodily tissues for therapeutic purposes. The invention relates more specifically to devices and methods for treating conditions associated with dementia, particularly Alzheimer's disease. The energy impulses (and/or fields) that are used to treat those conditions comprise electrical and/or electromagnetic energy, delivered non-invasively to the patient.
The use of electrical stimulation for treatment of medical conditions is well known. For example, electrical stimulation of the brain with implanted electrodes has been approved for use in the treatment of various conditions, including pain and movement disorders such as essential tremor and Parkinson's disease.
Another application of electrical stimulation of nerves is the treatment of radiating pain in the lower extremities by stimulating the sacral nerve roots at the bottom of the spinal cord [Paul F. WHITE, Shitong Li and Jen W. Chiu. Electroanalgesia: Its Role in Acute and Chronic Pain Management. Anesth Analg 92 (2001):505-513; U.S. Pat. No. 6,871,099 entitled Fully implantable microstimulator for spinal cord stimulation as a therapy for chronic pain, to Whitehurst, et al].
The form of electrical stimulation that is most relevant to the present invention is vagus nerve stimulation (VNS, also known as vagal nerve stimulation). It was developed initially for the treatment of partial onset epilepsy and was subsequently developed for the treatment of depression and other disorders. The left vagus nerve is ordinarily stimulated at a location within the neck by first surgically implanting an electrode there and then connecting the electrode to an electrical stimulator [U.S. Pat. No. 4,702,254 entitled Neurocybernetic prosthesis, to ZABARA; U.S. Pat. No. 6,341,236 entitled Vagal nerve stimulation techniques for treatment of epileptic seizures, to OSORIO et al; U.S. Pat. No. 5,299,569 entitled Treatment of neuropsychiatric disorders by nerve stimulation, to WERNICKE et al; G. C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain stimulation, vagal nerve stimulation and transcranial stimulation: An overview of stimulation parameters and neurotransmitter release. Neuroscience and Biobehavioral Reviews 33 (2009) 1042-1060; GROVES D A, Brown V. J. Vagal nerve stimulation: a review of its applications and potential mechanisms that mediate its clinical effects. Neurosci Biobehav Rev 29 (2005):493-500; Reese TERRY, Jr. Vagus nerve stimulation: a proven therapy for treatment of epilepsy strives to improve efficacy and expand applications. Conf Proc IEEE Eng Med Biol Soc. 2009; 2009:4631-4634; Timothy B. MAPSTONE. Vagus nerve stimulation: current concepts. Neurosurg Focus 25 (3, 2008):E9, pp. 1-4; ANDREWS, R. J. Neuromodulation. I. Techniques-deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation. Ann. N.Y. Acad. Sci. 993 (2003): 1-13; LABINER, D. M., Ahern, G. L. Vagus nerve stimulation therapy in depression and epilepsy: therapeutic parameter settings. Acta. Neurol. Scand. 115 (2007): 23-33].
Many such therapeutic applications of electrical stimulation involve the surgical implantation of electrodes within a patient. In contrast, devices used for the medical procedures that are disclosed herein do not involve surgery. Instead, the present devices and methods stimulate nerves by transmitting energy to nerves and tissue non-invasively. A medical procedure is defined as being non-invasive when no break in the skin (or other surface of the body, such as a wound bed) is created through use of the method, and when there is no contact with an internal body cavity beyond a body orifice (e.g, beyond the mouth or beyond the external auditory meatus of the ear). Such non-invasive procedures are distinguished from invasive procedures (including minimally invasive procedures) in that the invasive procedures insert a substance or device into or through the skin (or other surface of the body, such as a wound bed) or into an internal body cavity beyond a body orifice.
For example, transcutaneous electrical stimulation of a nerve is non-invasive because it involves attaching electrodes to the skin, or otherwise stimulating at or beyond the surface of the skin or using a form-fitting conductive garment, without breaking the skin [Thierry KELLER and Andreas Kuhn. Electrodes for transcutaneous (surface) electrical stimulation. Journal of Automatic Control, University of Belgrade 18(2, 2008):35-45; Mark R. PRAUSNITZ. The effects of electric current applied to skin: A review for transdermal drug delivery. Advanced Drug Delivery Reviews 18 (1996) 395-425]. In contrast, percutaneous electrical stimulation of a nerve is minimally invasive because it involves the introduction of an electrode under the skin, via needle-puncture of the skin.
Another form of non-invasive electrical stimulation is magnetic stimulation. It involves the induction, by a time-varying magnetic field, of electrical fields and current within tissue, in accordance with Faraday's law of induction. Magnetic stimulation is non-invasive because the magnetic field is produced by passing a time-varying current through a coil positioned outside the body, An electric field is induced at a distance causing electric current to flow within electrically conducting bodily tissue. The electrical circuits for magnetic stimulators are generally complex and expensive and use a high current impulse generator that may produce discharge currents of 5,000 amps or more, which is passed through the stimulator coil to produce a magnetic pulse. The principles of electrical nerve stimulation using a magnetic stimulator, along with descriptions of medical applications of magnetic stimulation, are reviewed in: Chris HOVEY and Reza Jalinous, The Guide to Magnetic Stimulation, The Magstim Company Ltd, Spring Gardens, Whitland, Carmarthenshire, SA34 0HR, United Kingdom, 2006. In contrast, the magnetic stimulators that are disclosed herein are relatively simpler devices that use considerably smaller currents within the stimulator coils. Accordingly, they are intended to satisfy the need for simple-to-use and less expensive non-invasive magnetic stimulation devices, for use in treating dementia, as well as use in treating other conditions.
Potential advantages of such non-invasive medical methods and devices relative to comparable invasive procedures are as follows. The patient may be more psychologically prepared to experience a procedure that is non-invasive and may therefore be more cooperative, resulting in a better outcome. Non-invasive procedures may avoid damage of biological tissues, such as that due to bleeding, infection, skin or internal organ injury, blood vessel injury, and vein or lung blood clotting. Non-invasive procedures are generally painless and may be performed without the dangers and costs of surgery. They are ordinarily performed even without the need for local anesthesia. Less training may be required for use of non-invasive procedures by medical professionals. In view of the reduced risk ordinarily associated with non-invasive procedures, some such procedures may be suitable for use by the patient or family members at home or by first-responders at home or at a workplace. Furthermore, the cost of non-invasive procedures may be significantly reduced relative to comparable invasive procedures.
In the present invention, noninvasive vagus nerve electrical stimulation and/or magnetic stimulation are used to treat neurodegenerative diseases. Neurodegenerative diseases result from the deterioration of neurons, causing brain dysfunction. The diseases are loosely divided into two groups—conditions affecting memory that are ordinarily related to dementia and conditions causing problems with movements. The most widely known neurodegenerative diseases include Alzheimer (or Alzheimer's) disease and its precursor mild cognitive impairment (MCI), Parkinson's disease (including Parkinson's disease dementia), and multiple sclerosis.
Less well-known neurodegenerative diseases include adrenoleukodystrophy, AIDS dementia complex, Alexander disease, Alper's disease, amyotrophic lateral sclerosis (ALS), ataxia telangiectasia, Batten disease, bovine spongiform encephalopathy, Canavan disease, cerebral amyloid angiopathy, cerebellar ataxia, Cockayne syndrome, corticobasal degeneration, Creutzfeldt-Jakob disease, diffuse myelinoclastic sclerosis, fatal familial insomnia, Fazio-Londe disease, Friedreich's ataxia, frontotemporal dementia or lobar degeneration, hereditary spastic paraplegia, Huntington disease, Kennedy's disease, Krabbe disease, Lewy body dementia, Lyme disease, Machado-Joseph disease, motor neuron disease, Multiple systems atrophy, neuroacanthocytosis, Niemann-Pick disease, Pelizaeus-Merzbacher Disease, Pick's disease, primary lateral sclerosis including its juvenile form, progressive bulbar palsy, progressive supranuclear palsy, Refsum's disease including its infantile form, Sandhoff disease, Schilder's disease, spinal muscular atrophy, spinocerebellar ataxia, Steele-Richardson-Olszewski disease, subacute combined degeneration of the spinal cord, survival motor neuron spinal muscular atrophy, Tabes dorsalis, Tay-Sachs disease, toxic encephalopathy, transmissible spongiform encephalopathy, Vascular dementia, and X-linked spinal muscular atrophy, as well as idiopathic or cryptogenic diseases as follows: synucleinopathy, progranulinopathy, tauopathy, amyloid disease, prion disease, protein aggregation disease, and movement disorder. A more comprehensive listing may be found at the web site (www) of the National Institute of Neurological Disorders and Stroke (ninds) of the National Institutes of Health (nih) of the United States government (gov). It is understood that such diseases often go by more than one name and that a disease classification may oversimplify pathologies that occur in combination or that are not archetypical.
Despite the fact that at least some aspect of the pathology of each of the neurodegenerative diseases mentioned above is different from the other diseases, their pathologies ordinarily share other features, so that they may be considered as a group. Furthermore, aspects of their pathologies that they have in common often make it possible to treat them with similar therapeutic methods. Thus, many publications describe features that neurodegenerative diseases have in common [Dale E. BREDESEN, Rammohan V. Rao and Patrick Mehlen. Cell death in the nervous system. Nature 443 (2006): 796-802; Christian HAASS. Initiation and propagation of neurodegeneration. Nature Medicine 16(11, 2010): 1201-1204; Eng H LO. Degeneration and repair in central nervous system disease. Nature Medicine 16(11, 2010):1205-1209; Daniel M. SKOVRONSKY, Virginia M.-Y. Lee, and John Q. TROJANOWSKI. Neurodegenerative Diseases New Concepts of Pathogenesis and Their Therapeutic Implications. Annu. Rev. Pathol. Mech. Dis. 1 (2006): 151-70; Michael T. LIN and M. Flint Beal. Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases. Nature 443 (2006): 787-795; Jorge J. PALOP, Jeannie Chin and Lennart Mucke. A network dysfunction perspective on neurodegenerative diseases. Nature 443 (2006): 768-773; David C. RUBINSZTEIN. The roles of intracellular protein-degradation pathways in neurodegeneration. Nature 443 (2006): 780-786].
The present invention is concerned primarily with the treatment of a particular class of neurodegenerative disease, namely, neurodegenerative dementias, among which Alzheimer (or Alzheimer's) disease (AD) is the most prevalent. However, it is understood that according to the previous paragraph, treatments that are disclosed here might be applicable to other neurodegenerative diseases as well.
Dementia is a clinical diagnosis that is based on evidence of cognitive dysfunction in both the patient's history and in successive mental status examinations. The diagnosis is made when there is impairment in two or more of the following: learning and retaining newly acquired information (episodic declarative memory); handling complex tasks and reasoning abilities (executive cognitive functions); visuospatial ability and geographic orientation; and language functions. The diagnosis may be made after excluding potentially treatable disorders that may otherwise contribute to cognitive impairment, such as depression, vitamin deficiencies, hypothyroidism, tumor, subdural hematomas, central nervous system infection, a cognitive disorder related to human immunodeficiency virus infection, adverse effects of prescribed medications, and substance abuse [McKHANN G, Drachman D, Folstein M, Katzman R, Price D, Stadlan E M. Clinical diagnosis of Alzheimer's disease: report of the NINCDS-ADRDA Work Group under the auspices of Department of Health and Human Services Task Force on Alzheimer's Disease. Neurology 34(7, 1984):939-44; David S. KNOPMAN. Alzheimer's Disease and other dementias. Chapter 409 (pp. 2274-2283) In: Goldman's Cecil Medicine, 24th Edn. (Lee Goldman and Andrew I. Schafer, Eds.). Philadelphia: Elsevier-Saunders, 2012; THOMPSON S B. Alzheimers Disease Comprehensive Review of Aetiology, Diagnosis, Assessment Recommendations and Treatment. Webmed Central AGING 2011; 2(3): WMC001681, pp. 1-42].
Dementia prevalence increases with age, from 5% of those aged 71-79 years to 37% of those aged 90 and older. However, despite their prevalence in old age, dementias such as Alzheimer's disease are not an integral part of the aging process [NELSON P T, Head E, Schmitt F A, Davis P R, Neltner J H, Jicha G A, Abner E L, Smith C D, Van Eldik Li, Kryscio R J, Scheff S W. Alzheimer's disease is not “brain aging”: neuropathological, genetic, and epidemiological human studies. Acta Neuropathol 121(5, 2011):571-87]. Genetics plays a role in early-onset AD (less than 1% of cases). The most powerful genetic risk factor for the more common forms of AD is the APOE e4 gene, one or more copies of which are carried by 60% of AD patients in some populations. Otherwise, the risk of AD may be increased by a low level of education, severe head injury, cerebrovascular disease, diabetes and obesity.
In the United States, the average annual cost of caring for a person with dementia in 2010 was $60,090. The total estimated worldwide annual costs of dementia were $604 billion in 2010, which exceeded the entire gross national product of Indonesia, Belgium, or Sweden [PLASSMAN B L, Langa K M, Fisher G G, Heeringa S G, Weir D R, Ofstedal M B, Burke J R, Hurd M D, Potter G G, Rodgers W L, Steffens D C, Willis R J, Wallace R B. Prevalence of dementia in the United States: the aging, demographics, and memory study. Neuroepidemiology 29(1-2, 2007):125-32; Anders WIMO and Martin Prince. Alzheimer's Disease International World Alzheimer Report 2010. The Global Economic Impact of Dementia. pp. 1-56. Alzheimer's Disease International (ADI). 64 Great Suffolk Street London SE 1 0BL, UK].
The principal diseases that cause dementia are three neurodegenerative diseases (Alzheimer's disease, Lewy body disease, and frontotemporal lobar degeneration) and cerebrovascular disease. In the United States, Alzheimer's disease accounts for approximately 70% of cases of dementia, and vascular dementia accounts for 17% of cases. Lewy body dementia and frontotemporal lobar dementia account for the remaining 13% of cases, along with less common causes (e.g., alcoholic/toxic dementia, traumatic brain injury, normal-pressure hydrocephalus, Parkinson's dementia, Creutzfeldt-Jakob disease, and undetermined etiology). In absolute numbers, 5.4 million Americans are currently living with Alzheimer's disease, and Lewy Body dementia affects 1.3 million Americans.
Patients with each type of dementia exhibit certain typical symptoms. In Alzheimer's disease, anterograde amnesia is a dominant symptom—loss of the ability to create new memories of events occurring after the onset of the disease. Dementia with Lewy bodies is characterized by parkinsonism, visual hallucinations, and a rapid-eye-movement sleep disorder. Frontotemporal lobar degeneration is characterized by prominent behavioral and personality changes or by prominent language difficulties early in the course of the disease. Cerebrovascular dementia, which may be a sequela of atherosclerosis, is due to one or more cerebral infarctions (ischemic strokes) in brain locations that are responsible for the cognitive deficits. The simultaneous presence of Alzheimer's disease with vascular dementia is common, and it may be difficult to distinguish these two dementia on the basis of symptoms alone.
Hour-to-hour and day-to-day changes in cognition may also be exhibited by individuals with dementia. Thus, caregivers of patients with dementia often notice that the patient may be confused and incoherent at one time, and only a few hours later, or the next day, the patient is alert and coherent. The time-course and situational antecedent of those so-called cognitive fluctuations may also be helpful in distinguishing one form of dementia from the others, using clinical scales have been developed to analyze such fluctuations (Clinician Assessment of Fluctuation, One Day Fluctuation Assessment Scale, Mayo Fluctuation Questionnaire). Dementia with Lewy bodies is associated with transient and spontaneous episodes of confusion and an inability to engage in meaningful cognitive activity, followed by reversion to a near normal level of function, often within hours. In contrast, cognitive fluctuations in Alzheimer's disease are often elicited by situations in which an underlying cognitive impairment manifests itself, typically as repetitiveness in conversation, forgetfulness in relation to a recent task or event, or other behavioral consequences of poor memory. In addition to this situational triggering aspect of a cognitive fluctuation in patients with Alzheimer's disease, the confusion is often a more enduring state shift (good days/bad days), rather than an hour-to-hour shift.
The mechanism of cognitive fluctuation is unknown, either for the hour-to-hour type that is common in dementia with Lewy bodies, or the day-to-day type that is not uncommon among Alzheimer patients. However, the mechanism is clearly different than the ones involved in circadian phenomena, such as “sundowning,” because the cognitive fluctuation need not occur around a particular time of day. Whatever the mechanism of cognitive fluctuations, it would be very beneficial to be able to prevent or reverse them, if only as a prophylactic or symptomatic treatment, so as to spare the patient and caregiver of the stress associated with fluctuating cognitive impairment as it relates to impairment of activities of daily living [Jorge J. PALOP, Jeannie Chin and Lennart Mucke. A network dysfunction perspective on neurodegenerative diseases. Nature 443(7113, 2006):768-73; WALKER M P, Ayre G A, Cummings J L, Wesnes K, McKeith I G, O'Brien J T, Ballard C G. The Clinician Assessment of Fluctuation and the One Day Fluctuation Assessment Scale. Two methods to assess fluctuating confusion in dementia. Br J Psychiatry 177 (2000):252-6; BRADSHAW J, Saling M, Hopwood M, Anderson V, Brodtmann A. Fluctuating cognition in dementia with Lewy bodies and Alzheimer's disease is qualitatively distinct. J Neurol Neurosurg Psychiatry 75(3, 2004):382-7; BALLARD C, Walker M, O'Brien J, Rowan E, McKeith I. The characterisation and impact of ‘fluctuating’ cognition in dementia with Lewy bodies and Alzheimer's disease. Int J Geriatr Psychiatry 16(5, 2001):494-8; CUMMINGS J L. Fluctuations in cognitive function in dementia with Lewy bodies. Lancet Neurol 3(5, 2004):266; David R. LEE, John-Paul Taylor, Alan J. Thomas. Assessment of cognitive fluctuation in dementia: a systematic review of the literature. International Journal of Geriatric Psychiatry 27(10, 2012): 989-998; BACHMAN D, Rabins P. “Sundowning” and other temporally associated agitation states in dementia patients. Annu Rev Med 57 (2006):499-511].
As described above, dementia is a clinical diagnosis that is based on evidence of cognitive dysfunction in both the patient's history and in successive mental status examinations. With the ability to better stage the progression of dementia, treatment might be justified at stages prior to actual onset of the dementia. In particular, the present invention might best be used early in the course of the disease progression, such that treatment could be directed to slowing, stopping, or even reversing the pathophysiological processes underlying the dementia. Thus, the present invention contemplates treatments even when the patient exhibits prodromal symptoms or when the patient has been diagnosed with mild cognitive impairment (MCI) [DeCARLI C. Mild cognitive impairment: prevalence, prognosis, aetiology, and treatment. Lancet Neurol 2(1, 2003):15-21; MAYEUX R. Clinical practice. Early Alzheimer's disease. N Engl J Med 362(23, 2010):2194-2201; WILSON R S, Leurgans S E, Boyle P A, Bennett D A. Cognitive decline in prodromal Alzheimer disease and mild cognitive impairment. Arch Neurol 68(3, 2011):351-356].
Early staging of the patient's disease progression makes use of biomarkers, which are cognitive, physiological, biochemical, and anatomical variables that can be measured in a patient that indicate the progression of a dementia such as AD. The most commonly measured biomarkers for AD include decreased Aβ42 in the cerebrospinal fluid (CSF), increased CSF tau, decreased fluorodeoxyglucose uptake on PET (FDG-PET), PET amyloid imaging, and structural MRI measures of cerebral atrophy. Use of biomarkers to stage AD has developed to the point that biomarkers can be used with revised criteria for diagnosing the disease [MASDEU J C, Kreisl W C, Berman K F. The neurobiology of Alzheimer disease defined by neuroimaging. Curr Opin Neurol 25(4, 2012):410-420; DUBOIS B, Feldman H H, Jacova C, Dekosky S T, Barberger-Gateau P, Cummings J, Delacourte A, Galasko D, Gauthier S, Jicha G, Meguro K, O'brien J, Pasquier F, Robert P, Rossor M, Salloway S, Stern Y, Visser P J, Scheltens P. Research criteria for the diagnosis of Alzheimer's disease: revising the NINCDS-ADRDA criteria. Lancet Neurol 6(8, 2007):734-46; GAUTHIER S, Dubois B, Feldman H, Scheltens P. Revised research diagnostic criteria for Alzheimer's disease. Lancet Neurol 7 (8, 2008): 668-670].
In the remainder of this background section, current methods of treating AD are described. As summarized here, they include methods to treat cognitive symptoms of AD patients, as well as methods that are intended to treat the underlying pathophysiological progression of AD. Because the methods described in the publications cited below have not been demonstrated to exhibit more than very modest success in treating only symptoms of AD, and no method is known to stop the progression of AD, additional methods are clearly needed, which motivates the invention that is disclosed here. Because the disclosure involves vagus nerve stimulation, the effect of stimulation on the patient's locus ceruleus, and consequences of that effect, the literature relevant to those subjects is emphasized in what follows.
Before the currently favored amyloid cascade hypothesis of AD (and subsequent variants of that hypothesis), the focus of AD research was the search for a clearly defined neurochemical abnormality in AD patients, which would provide the basis for the development of rational therapeutic interventions that are analogous to levodopa treatment of Parkinson's disease. This led to the cholinergic hypothesis of Alzheimer's disease, which proposed that degeneration of cholinergic neurons in the basal forebrain and the associated loss of cholinergic neurotransmission in the cerebral cortex and other areas contributed significantly to the deterioration in cognitive function seen in patients with Alzheimer's disease. The symptomatic drug treatments that arose from that research are currently the mainstay of AD treatment, even though their effectiveness is very modest, and no drug delays the progression of the disease. Approved drugs for the symptomatic treatment of AD modulate neurotransmitters—either acetylcholine or glutamate: cholinesterase inhibitors (tacrine, rivastigmine, galantamine and donepezil) and partial N-methyl-D-aspartate antagonists (memantine) [FRANCIS P T, Ramírez M J, Lai M K. Neurochemical basis for symptomatic treatment of Alzheimer's disease. Neuropharmacology 59(4-5, 2010):221-229; FRANCIS P T, Palmer A M, Snape M, Wilcock G K. The cholinergic hypothesis of Alzheimer's disease: a review of progress. J Neurol Neurosurg Psychiatry 66(2, 1999):137-47; MESULAM M. The cholinergic lesion of Alzheimer's disease: pivotal factor or side show? Learn Mem 11(1, 2004):43-49].
The symptomatic treatment of AD by modulating neurotransmitters other than acetylcholine or glutamate has also been considered. One such neurotransmitter is norepinephrine (noradrenaline), which in the brain is principally synthesized in the locus ceruleus. A rationale for therapeutic modulation of norepinephrine levels has been that in AD, there is loss of noradrenergic neurons in the locus ceruleus, and the treatment would compensate for that loss [HAGLUND M, Sjöbeck M, Englund E. Locus ceruleus degeneration is ubiquitous in Alzheimer's disease: possible implications for diagnosis and treatment. Neuropathology 26(6, 2006):528-32; SAMUELS E R, Szabadi E. Functional neuroanatomy of the noradrenergic locus coeruleus: its roles in the regulation of arousal and autonomic function part II: physiological and pharmacological manipulations and pathological alterations of locus coeruleus activity in humans. Curr Neuropharmacol 6(3, 2008):254-85; Patricia SZOT. Common factors among Alzheimer's disease, Parkinson's disease, and epilepsy: Possible role of the noradrenergic nervous system. Epilepsia 53(Suppl. 1, 2012):61-66].
Accordingly, several investigators proposed to increase brain norepinephrine as a therapy for AD patients [E M VAZEY, V K Hinson, A C Granholm, M A Eckert, G A Jones. Norepinephrine in Neurodegeneration: A Coerulean Target. J Alzheimers Dis Parkinsonism 2(2, 2012):1000e114, pp. 1-3]. Administration of norepinephrine itself is not feasible as a method for increasing its levels in the central nervous system because norepinephrine, as with other catecholamines, cannot cross the blood-brain barrier. Many other drugs such as amphetamines and methylphenidate can increase norepinephrine brain levels, but they affect other neurotransmitter systems as well and have significant side effects. Consequently, less direct methods have been used or suggested as ways to increase norepinephrine levels in the central nervous system, or to activate adrenergic signaling. They include the use of special drugs that mimic norepinephrine, that serve as precursors of norepinephrine, that block the reuptake of norepinephrine, and that serve as adrenoceptor antagonists that enhances norepinephrine release [MISSONNIER P, Ragot R, Derouesné C, Guez D, Renault B. Automatic attentional shifts induced by a noradrenergic drug in Alzheimer's disease: evidence from evoked potentials. Int J Psychophysiol 33(3, 1999): 243-51; FRIEDMAN J I, Adler D N, Davis K L. The role of norepinephrine in the pathophysiology of cognitive disorders: potential applications to the treatment of cognitive dysfunction in schizophrenia and Alzheimer's disease. Biol Psychiatry. 46(9, 1999):1243-52; KALININ S, Polak P E, Lin S X, Sakharkar A J, Pandey S C, Feinstein D L. The noradrenaline precursor L-DOPS reduces pathology in a mouse model of Alzheimer's disease. Neurobiol Aging 33(8, 2012):1651-1663; MOHS, R. C., Shiovitz, T. M., Tariot, P. N., Porsteinsson, A. P., Baker, K. D., Feldman, P. D., 2009. Atomoxetine augmentation of cholinesterase inhibitor therapy in patients with Alzheimer disease: 6-month, randomized, double-blind, placebo-controlled, parallel-trial study. Am. J. Geriatr. Psychiatry 17, 752-759; SCULLION G A, Kendall D A, Marsden C A, Sunter D, Pardon M C. Chronic treatment with the a2-adrenoceptor antagonist fluparoxan prevents age-related deficits in spatial working memory in APP×PS1 transgenic mice without altering β-amyloid plaque load or astrocytosis. Neuropharmacology 60(2-3, 2011):223-34]. Other agents that are thought to alter norepinephrine levels, via locus ceruleus activity, include chronic stress, chronic opiate treatment, and anti-depressant treatment [NESTLER E J, Alreja M, Aghajanian G K. Molecular control of locus coeruleus neurotransmission. Biol Psychiatry 46(9, 1999):1131-1139; SAMUELS, E. R., and Szabadi, E. Functional neuroanatomy of the noradrenergic locus coeruleus: its roles in the regulation of arousal and autonomic function part II: physiological and pharmacological manipulations and pathological alterations of locus coeruleus activity in humans. Curr. Neuropharmacol. 6 (2008), 254-285].
However, for several reasons, it is not settled that a pharmacologically-induced increase of norepinephrine, or increased signaling through the adrenergic receptors in the central nervous system, will substantially benefit AD patients. First, in patients with AD, clonidine (a centrally acting alpha2 adrenergic agonist) was reported to have no effect on cognitive functions, and may even impair sustained attention and memory. Another putative alpha2-adrenoceptor agonist, guanfacine, has consistently been shown to be without effect on cognitive functions. Thus, administration of clonidine or guanfacine does not appear to provide any consistent improvement in cognitive functions, either in normal subjects or in patients with AD or other cognitive impairments. On the other hand, the alpha2-adrenoceptor antagonist, idazoxan, improved planning, sustained attention, verbal fluency, and episodic memory but impaired spatial working memory in patients with dementia of the frontal type [MARIEN M R, Colpaert F C, Rosenquist A C. Noradrenergic mechanisms in neurodegenerative diseases: a theory. Brain Res Brain Res Rev 45(1, 2004):38-78].
Second, norepinephrine significantly worsens agitation and anxiety in AD patients, such that any potential benefits of increased norepinephrine levels may be offset by behavioral side effects, as well as cardiovascular side effects [HERRMANN N, Lanctôt K L, Khan L R. The role of norepinephrine in the behavioral and psychological symptoms of dementia. J Neuropsychiatry Clin Neurosci 16(3, 2004):261-76; PESKIND, E. R., Tsuang, D. W., Bonner, L. T., Pascualy, M., Riekse, R. G., Snowden, M. B., Thomas, R., Raskind, M. A. Propranolol for disruptive behaviors in nursing home residents with probable or possible Alzheimer disease: a placebo-controlled study. Alzheimer Dis. Assoc. Disord. 19 (2005): 23-28].
Third, loss of locus ceruleus cells in AD may lead to compensatory production of norepinephrine in other cells, such that there may actually be an increase in norepinephrine levels in some AD patients [Fitzgerald P J. Is elevated norepinephrine an etiological factor in some cases of Alzheimer's disease? Curr Alzheimer Res 7(6, 2010):506-16; ELROD R, Peskind E R, DiGiacomo L, Brodkin K I, Veith R C, Raskind M A. Effects of Alzheimer's disease severity on cerebrospinal fluid norepinephrine concentration. Am J Psychiatry 154(1, 1997):25-30].
Even if there is a decrease in overall brain norepinephrine levels in AD, this decrease does not necessarily occur uniformly among brain regions that are modulated by the locus ceruleus, and patterns of compensatory receptor alterations may also be complicated, with selective decreases and increases of noradrenergic receptors subtypes in different regions of the brain [HOOGENDIJK W J, Feenstra M G, Botterblom M H, Gilhuis J, Sommer I E, Kamphorst W, Eikelenboom P, Swaab D F. Increased activity of surviving locus ceruleus neurons in Alzheimer's disease. Ann Neurol 45(1, 1999):82-91; SZOT P, White S S, Greenup J L, Leverenz J B, Peskind E R, Raskind M A. Compensatory changes in the noradrenergic nervous system in the locus coeruleus and hippocampus of postmortem subjects with Alzheimer's disease and dementia with Lewy Bodies. J Neurosci 26 (2006):467-478; SZOT P, White S S, Greenup J L, Leverenz J B, Peskind E R, Raskind M A. Changes in adrenoreceptors in the prefrontal cortex of subjects with dementia: evidence of compensatory changes. Neuroscience 146 (2007):471-480].
Therefore, what is needed is not a pharmacological method that increases norepinephrine levels indiscriminately throughout the central nervous system of AD patients, but rather a method that can selectively increase (or decrease) the norepinephrine levels only where it is needed. This is true whether the increase is intended to improve cognition or whether the increase in norepinephrine levels is intended to prevent, delay or antagonize pathological biochemical changes that occur in the brains of AD patients [COUNTS S E, Mufson E J. Noradrenaline activation of neurotrophic pathways protects against neuronal amyloid toxicity. J Neurochem 113(3, 2010):649-60; WENK G L, McGann K, Hauss-Wegrzyniak B, Rosi S. The toxicity of tumor necrosis factor-alpha upon cholinergic neurons within the nucleus basalis and the role of norepinephrine in the regulation of inflammation: implications for Alzheimer's disease. Neuroscience 121(3, 2003):719-29; KALININ S, Gavrilyuk V, Polak P E, Vasser R, Zhao J, Heneka M T, Feinstein D L. Noradrenaline deficiency in brain increases beta-amyloid plaque burden in an animal model of Alzheimer's disease. Neurobiol Aging 28(8, 2007):1206-1214; HENEKA M T, Ramanathan M, Jacobs A H, Dumitrescu-Ozimek L, Bilkei-Gorzo A, Debeir T, Sastre M, Galldiks N, Zimmer A, Hoehn M, Heiss W D, Klockgether T, Staufenbiel M. Locus ceruleus degeneration promotes Alzheimer pathogenesis in amyloid precursor protein 23 transgenic mice. J. Neurosci. 26(5, 2006):1343-54; HENEKA M T, Nadrigny F, Regen T, Martinez-Hernandez A, Dumitrescu-Ozimek L, Terwel D, Jardanhazi-Kurutz D, Walter J, Kirchhoff F, Hanisch U K, Kummer M P. Locus ceruleus controls Alzheimer's disease pathology by modulating microglial functions through norepinephrine. Proc Natl Acad Sci USA. 107(13, 2010):6058-6063; JARDANHAZI-KURUTZ D, Kummer M P, Terwel D, Vogel K, Thiele A, Heneka M T. Distinct adrenergic system changes and neuroinflammation in response to induced locus ceruleus degeneration in APP/PS1 transgenic mice. Neuroscience 176 (2011):396-407; YANG J H, Lee E O, Kim S E, Suh Y H, Chong Y H. Norepinephrine differentially modulates the innate inflammatory response provoked by amyloid-R peptide via action at β-adrenoceptors and activation of cAMP/PKA pathway in human THP-1 macrophages. Exp Neurol 236(2, 2012):199-206; KONG Y, Ruan L, Qian L, Liu X, Le Y. Norepinephrine promotes microglia to uptake and degrade amyloid beta peptide through upregulation of mouse formyl peptide receptor 2 and induction of insulin-degrading enzyme. J Neurosci 30(35, 2012):11848-11857; KALININ S, Polak P E, Lin S X, Sakharkar A J, Pandey S C, Feinstein D L. The noradrenaline precursor L-DOPS reduces pathology in a mouse model of Alzheimer's disease. Neurobiol Aging 33(8, 2012):1651-1663; HAMMERSCHMIDT T, Kummer M P, Terwel D, Martinez A, Gorji A, Pape H C, Rommelfanger K S, Schroeder J P, Stoll M, Schultze J, Weinshenker D, Heneka M T. Selective Loss of Noradrenaline Exacerbates Early Cognitive Dysfunction and Synaptic Deficits in APP/PS1 Mice. Biol Psychiatry. 2012 Aug. 9. Epub ahead of print, pp. 1-10; O'DONNELL J, Zeppenfeld D, McConnell E, Pena S, Nedergaard M. Norepinephrine: A Neuromodulator That Boosts the Function of Multiple Cell Types to Optimize CNS Performance. Neurochem Res. 2012 Jun. 21. (Epub ahead of print}, pp. 1-17]. Psychotropic medications are also used in conjunction with the neurotransmitter modulators to treat secondary symptoms of AD such as depression, agitation, and sleep disorders [Julius POPP and Sonke Arlt. Pharmacological treatment of dementia and mild cognitive impairment due to Alzheimer's disease. Current Opinion in Psychiatry 24 (2011):556-561; Fadi MASSOUD and Gabriel C Leger. Pharmacological treatment of Alzheimer disease. Can J. Psychiatry. 56(10, 2011):579-588; Carl H. SADOWSKY and James E. Galvin. Guidelines for the management of cognitive and behavioral problems in dementia. J Am Board Fam Med 25 (2012):350-366].
Therapies based on nutrition, lifestyle modification, herbal or dietary supplements (e.g., Huperzine A), brain exercises, and other integrative methods have also been proposed [Dharma Singh KHALSA. Alzheimer Disease. pp. 78-90 (Chapter 9) In: Integrative Medicine, 3rd Ed. (David Rakel, ed.) Philadelphia, Pa.: Elsevier Saunders, 2012; Clive BALLARD, Zunera Khan, Hannah Clack, and Anne Corbett. Nonpharmacological treatment of Alzheimer disease. The Canadian Journal of Psychiatry 56(10, 2011): 589-595; DAVIGLUS M L, Bell C C, Berrettini W, Bowen P E, Connolly E S, Cox N J, Dunbar-Jacob J M, Granieri E C, Hunt G, McGarry K, Patel D, Potosky A L, Sanders-Bush E, Silberberg D, Trevisan M. NIH State-of-the-Science Conference Statement: Preventing Alzheimer's Disease and Cognitive Decline. NIH Consens State Sci Statements 27(4, 2010), pp. 1-121].
Therapies directed to modifying AD progression itself are considered investigational. These include treatment of the intense inflammation that occurs in the brains of patients with AD, estrogen therapy, use of free-radical scavengers, therapies designed to decrease toxic amyloid fragments in the brain (vaccination, anti-amyloid antibodies, selective amyloid-lowering agents, chelating agents to prevent amyloid polymerization, brain shunting to improve removal of amyloid, and beta-secretase inhibitors to prevent generation of the A-beta amyloid fragment), and agents that may prevent or reverse excess tau phosphorylation and thereby diminish formation of neurofibrillary tangles. Some agents, such as retinoids, may target multiple aspects of AD pathogenesis [TAYEB H O, Yang H D, Price B H, Tarazi F I. Pharmacotherapies for Alzheimer's disease: beyond cholinesterase inhibitors. Pharmacol Ther 134(1, 2012):8-25; LEMER A J, Gustaw-Rothenberg K, Smyth S, Casadesus G. Retinoids for treatment of Alzheimer's disease. Biofactors 38(2, 2012):84-89; KURZ A, Perneczky R. Novel insights for the treatment of Alzheimer's disease. Prog Neuropsychopharmacol Biol Psychiatry 35(2, 2011):373-379; MINATI L, Edginton T, Bruzzone M G, Giaccone G. Current concepts in Alzheimer's disease: a multidisciplinary review. Am J Alzheimers Dis Other Demen 24(2, 2009):95-121].
However, it is increasingly recognized that a single target or pathogenic pathway for the treatment of AD is unlikely to be identified. The best strategy is thought to be a multi-target therapy that includes multiple types of treatments [MANGIALASCHE F, Solomon A, Winblad B, Mecocci P, Kivipelto M. Alzheimer disease: clinical trials and drug development. Lancet Neurol 9(7, 2010):702-716]. Targets in that multi-target approach will include inflammatory pathways, and several therapeutic agents have been proposed to target them—nonsteroidal anti-inflammatory drugs, statins, RAGE antagonists and antioxidants [STUCHBURY G, Münch G. Alzheimer associated inflammation, potential drug targets and future therapies. J Neural Transm. 2005 March; 112(3):429-53 Joseph BUTCHART and Clive Holmes. Systemic and Central Immunity in Alzheimer's Disease: Therapeutic Implications. CNS Neuroscience & Therapeutics 18 (2012): 64-76]. Another such agent, Etanercept, targets TNF-alpha, but its use has the disadvantage that because it does not pass the blood-brain barrier (BBB), its administration is via a painful spinal route or via an experimental method to get through the BBB [U.S. Pat. No. 7,640,062, entitled Methods and systems for management of alzheimer's disease, to SHALEV]. One TNF-inhibitor that does not have this disadvantage is thalidomide [Tweedie D, Sambamurti K, Greig N H: TNF-alpha Inhibition as a Treatment Strategy for Neurodegenerative Disorders: New Drug Candidates and Targets. Curr Alzheimer Res 2007, 4(4):375-8]. However, thalidomide is well known by the public to cause birth defects, and in a small trial, its use did not appear to improve cognition in AD patients [Peggy PECK. IADRD: Pilot Study of Thalidomide for Alzheimer's Disease Fails to Detect Cognitive Benefit but Finds Effect on TNF-alpha. Doctor's Guide Global Edition, Jul. 26, 2002].
Various devices have been proposed to restore or enhance cognition, including cognition of AD patients [Mijail Demian SERRUYA and Michael J. Kahana. Techniques and devices to restore cognition. Behav Brain Res 192(2, 2008): 149-165]. Deep brain electrical stimulation has been generally unsuccessful or counterproductive in attempting to enhance the memory of AD patients. However, improved verbal recall has been observed in one case study in which deep-brain stimulation of the hypothalamus and fornix was used to treat morbid obesity [HAMANI C, McAndrews M P, Cohn M, Oh M, Zumsteg D, Shapiro C M, Wennberg R A, Lozano A M. Memory enhancement induced by hypothalamic/fornix deep brain stimulation. Ann Neurol 63 (2008):119-23; Adrian W. LAXTON and Andres M. Lozano. Deep brain stimulation for the treatment of Alzheimer disease and dementias. World Neurosurg. (2012), pp. 1-8]. Entorhinal, but not hippocampal, deep brain stimulation has also been found to improve memory used in spatial navigation. Authors of that investigation suggest that in using neuroprosthetic devices for purposes of cognitive enhancement, stimulation may not need to be applied continuously, but instead only when patients are attempting to learn important information. They also suggest that resetting of the phase of the theta rhythm in the EEG (3-8 Hz) improves memory performance, as has been observed in animal experiments [Nanthia SUTHANA, Zulfi Haneef, John Stern, Roy Mukamel, Eric Behnke, Barbara Knowlton and Itzhak Fried. Memory enhancement and deep-brain stimulation of the entorhinal area. N Engl J Med 366 (2012):502-10; LEMON N, Aydin-Abidin S, Funke K, Manahan-Vaughan D. Locus coeruleus activation facilitates memory encoding and induces hippocampal LTD that depends on beta-adrenergic receptor activation. Cereb Cortex 19(12, 2009):2827-37].
Magnetic stimulation of AD patients has also been performed, but its use has been intended only to affect cognitive skills and only using transcranial magnetic stimulation [Mamede de CARVALHO, Alexandre de Mendonça, Pedro C. Miranda, Carlos Garcia and Maria Lourdes Sales Luís. Magnetic stimulation in Alzheimer's disease. Journal of Neurology 244 (1997, 5): 304-307; COTELLI M, Manenti R, Cappa S F, Zanetti O, Miniussi C. Transcranial magnetic stimulation improves naming in Alzheimer disease patients at different stages of cognitive decline. Eur J. Neurol. 15(12, 2008):1286-92; GUSE B, Falkai P, Wobrock T. Cognitive effects of high-frequency repetitive transcranial magnetic stimulation: a systematic review. J Neural Transm. 117(1, 2010):105-22; Raffaele NARDONE, Jurgen Bergmann, Monica Christova, Francesca Caleri, Frediano Tezzon, Gunther Ladurner, Eugen Trinka and Stefan Golaszewski. Effect of transcranial brain stimulation for the treatment of Alzheimer disease: A review. International Journal of Alzheimer's Disease 2012, Article ID 687909: pp. 1-5; Raffaele NARDONE, Stefan Golaszewski, Gunther Ladurner, Frediano Tezzon, and Eugen Trinka. A Review of Transcranial Magnetic Stimulation in the in vivo Functional Evaluation of Central Cholinergic Circuits in Dementia. Dement Geriatr Cogn Disord 32 (2011):18-25].
A method of using vagal nerve stimulation to treat AD symptoms was disclosed in U.S. Pat. No. 5,269,303, entitled Treatment of dementia by nerve stimulation, to WERNICKE et al. It is directed to “a symptom of dementia” which was described as being either paroxysmal activity exhibited in the patient's EEG or the level of alertness of the patient, but not to cognition per se.
In 2002, it was reported that electrical stimulation of the vagus nerve has a beneficial effect on cognition in patients with AD [SJOGREN M J, Hellström P T, Jonsson M A, Runnerstam M, Silander H C, Ben-Menachem E. Cognition-enhancing effect of vagus nerve stimulation in patients with Alzheimer's disease: a pilot study. J Clin Psychiatry 63(11, 2002):972-80]. The rationale for that trial was that vagus nerve stimulation had previously been found to enhance the cognitive abilities of patients that were undergoing vagus nerve stimulation for other conditions such as epilepsy and depression, as well as enhanced cognitive abilities observed in animal studies. Results concerning the AD patients' improved cognitive abilities over a longer period of time, along with improvement in tau protein of cerebrospinal fluid, were subsequently reported [MERRILL C A, Jonsson M A, Minthon L, Ejnell H, C-son Silander H, Blennow K, Karlsson M, Nordlund A, Rolstad S, Warkentin S, Ben-Menachem E, Sjögren M J. Vagus nerve stimulation in patients with Alzheimer's disease: Additional follow-up results of a pilot study through 1 year. J Clin Psychiatry. 2006 August; 67(8):1171-8]. Those results were immediately greeted with skepticism, particularly the purported changes in tau protein, because there was no control group and the number of patients was small [Theresa DEFINO. Symptoms stable in AD patients who underwent vagus nerve stimulation. Neurology Today 6(21, 2006):14-15].
Stimulation of the vagus nerve to treat at least the symptomatic cognitive aspects of dementia might be more effective than stimulation of nerves found in locations such as the spine, forehead, and earlobes [CAMERON M H, Lonergan E, Lee H. Transcutaneous Electrical Nerve Stimulation (TENS) for dementia. Cochrane Database of Systematic Reviews 2003, Issue 3. Art. No.: CD004032. (2009 update); Erik J. A. SCHERDER, Marijn W. Luijpen, and Koene R. A. van Dijk. Activation of the dorsal raphe nucleus and locus coeruleus by transcutaneous electrical nerve stimulation in Alzheimer's disease: a reconsideration of stimulation-parameters derived from animal studies. Chinese Journal of Physiology 46(4, 2003): 143-150]. However, BOON and colleagues dispute the claim that vagus nerve stimulation with prevailing stimulation parameters can enhance even the cognitive abilities of human patients, although they do conclude that such stimulation can improve cognition in animal models [Paul BOON, Ine Moors, Veerle De Herdt, Kristl Vonck. Vagus nerve stimulation and cognition. Seizure 15 (2006), 259-263]. In fact, in humans, vagus nerve stimulation impairs cognitive flexibility and creative thinking [GHACIBEH G A, Shenker J I, Shenal B, Uthman B M, Heilman K M. Effect of vagus nerve stimulation on creativity and cognitive flexibility. Epilepsy Behav 8(4, 2006):720-725]. Furthermore, it has no effect on learning, but it might enhance memory consolidation, which leads to improved retention [GHACIBEH G A, Shenker J I, Shenal B, Uthman B M, Heilman K M. The influence of vagus nerve stimulation on memory. Cogn Behav Neurol 19(3, 2006):119-22; CLARK K B, Naritoku D K, Smith D C, Browning R A, Jensen R A. Enhanced recognition memory following vagus nerve stimulation in human subjects. Nature Neurosci 2 (1999):94-98]. Among different types of memories, vagus nerve stimulation is reported to improve only verbal recognition memory [McGLONE J, Valdivia I, Penner M, Williams J, Sadler R M, Clarke D B. Quality of life and memory after vagus nerve stimulator implantation for epilepsy. Can J Neurol Sci 35(3, 2008):287-96]. However, most such investigations have been performed on patients with electrodes implanted to control epilepsy, so patients with Alzheimer's disease were not included in the studies.
The effects of vagus nerve stimulation on the cognition of animal models are given in experiments described in the following publications. The animal experiments show generally that it may be possible to promote cognition using vagus nerve stimulation, which suggests that failure in the above-mentioned human experiments might be attributable to using stimulation parameters that treat epilepsy or depression, instead of parameters that preferentially enhance cognition. Vagus nerve stimulation was shown to activate the locus ceruleus and to increase norepinephrine output into the basolateral amygdala and hippocampus in rats [NARITOKU D K, Terry W J, Helfert R H. Regional induction of fos immunoreactivity in the brain by anticonvulsant stimulation of the vagus nerve. Epilepsy Res 22(1, 1995):53-62; HASSERT D L, Miyashita T, Williams C L. The effects of peripheral vagal nerve stimulation at a memory-modulating intensity on norepinephrine output in the basolateral amygdala. Behav Neurosci 118(1, 2004):79-88; CHEN C C, Williams C L. Interactions between epinephrine, ascending vagal fibers, and central noradrenergic systems in modulating memory for emotionally arousing events. Front Behav Neurosci 6:35. Epub 2012 Jun. 28, pp. 1-20].
In a rat model of traumatic brain injury, it was shown that vagus nerve stimulation facilitated both the rate of recovery and the extent of motor and cognitive recovery [SMITH D C, Modglin A A, Roosevelt R W, Neese S L, Jensen R A, Browning R A, et al. Electrical stimulation of the vagus nerve enhances cognitive and motor recovery following moderate fluid percussion injury in the rat. J Neurotrauma 22(12, 2005):1485-1502]. Electrical stimulation of the vagus nerve (VNS) delivered at a moderate intensity following a learning experience enhances memory in laboratory rats, while VNS at lower or higher intensities has little or no effect, which appears to involve modulating synaptic plasticity in the hippocampus [ZUO Y, Smith D C, Jensen R A. Vagus nerve stimulation potentiates hippocampal LTP in freely moving rats. Physiol Behav 90(4, 2007):583-589]. More generally, vagus nerve stimulation modulates norepinephrine levels via effects on the locus ceruleus [DORR A E, Debonnel G. Effect of vagus nerve stimulation on serotonergic and noradrenergic transmission. J Pharmacol Exp Ther 318(2, 2006):890-898; MANTA S, Dong J, Debonnel G, Blier P. Enhancement of the function of rat serotonin and norepinephrine neurons by sustained vagus nerve stimulation. J Psychiatry Neurosci 34(4, 2009):272-80; SHEN H, Fuchino Y, Miyamoto D, Nomura H, Matsuki N. Vagus nerve stimulation enhances perforant path-CA3 synaptic transmission via the activation of β-adrenergic receptors and the locus coeruleus. Int J Neuropsychopharmacol 15(4, 2012):523-30].
Otherwise, the only mechanism by which vagus nerve stimulation has been suggested to affect synaptic activity (e.g., seizures) is via its effect on cerebral circulation [HENRY T R, Bakay R A, Pennell P B, Epstein C M, Votaw J R. Brain blood-flow alterations induced by therapeutic vagus nerve stimulation in partial epilepsy: II. prolonged effects at high and low levels of stimulation. Epilepsia 45(9, 2004):1064-1070].
In a commonly assigned, co-pending patent application (Publication US 20110152967, entitled Non-invasive treatment of neurodegenerative disease, to SIMON et al), Applicants disclosed six novel mechanisms by which stimulation of the vagus nerve may be used to treat the underlying pathophysiology of AD: (1) stimulate the vagus nerve in such a way as to enhance the availability or effectiveness of TGF-beta or other anti-inflammatory cytokines; (2) stimulate the vagus nerve in such a way as to enhance the availability or effectiveness of retinoic acid; (3) stimulate the vagus nerve in such a way as to promote the expression of the neurotrophic factors such as BDNF; (4) stimulate the vagus nerve to modulate the capacity of TNF-alpha to function as a gliotransmitter, including modulating the activity of the cells between which TNF-related gliotransmission occurs; (5) stimulate the vagus nerve to modulate the degradation of TNF-alpha, and/or modify the activity of existing TNF-alpha molecules as a pro-inflammatory mediator; and (6) stimulate the vagus nerve in such a way as to suppress the release or effectiveness of pro-inflammatory cytokines, through a mechanism that is distinct from the one proposed by TRACEY and colleagues. Thus, U.S. Pat. No. 6,610,713 and U.S. Pat. No. 6,838,471, entitled Inhibition of inflammatory cytokine production by cholinergic agonists and vagus nerve stimulation, to TRACEY, mention treatment of neurodegenerative diseases within a long list of diseases, in connection with the treatment of inflammation through stimulation of the vagus nerve. However, there is no mention or suggestion by TRACEY that his methods are intended to modulate the activity of anti-inflammatory cytokines, and in fact, his disclosures disclaim a role for antiinflammatory cytokines as mediators of inflammation through stimulation of the vagus nerve.
In the present application, additional methods and devices for the treatment or prevention of dementia, particularly Alzheimer's disease, are disclosed. The disclosed method does not increase norepinephrine levels indiscriminately throughout the CNS of AD patients, but instead preferentially increases the norepinephrine levels where it is needed, through selection of appropriate vagus nerve stimulation parameters, which may be adjusted on an individualized basis and on the basis of progression of the disease. The method prevents loss of the locus ceruleus and takes into account the existence of so-called resting state brain networks, particularly the default mode network and the ventral attention network. According to the invention, site-preferential modulation of norepinephrine levels by vagus nerve stimulation prevents, delays or antagonizes pathological biochemical changes that occur in the brains of AD patients and that lead to a loss of locus ceruleus cells. The stimulation may also enhance cognition, particularly in patients who are experiencing cognitive fluctuations.